Search Results (771)

The peripheries of rare-metal metallogenic systems frequently host skarn-type or hydrothermal vein-type Pb-Zn deposits, though their genetic connections with parental systems remain debated. The newly identified Gariatong W-Mo polymetallic metallogenic system in the Lhasa Terrane displays well-defined Nb-Ta-Rb, Mo-W, W-Mo, W-Bi, and Pb-Zn-Ag metallogenic zoning, establishing it as an exemplary site for investigating genetic relationships between Pb-Zn and rare-metal mineralization. This investigation targets skarn-type Pb-Zn deposits spatially associated with rare-metal orebodies at Gariatong, utilizing integrated analytical approaches, including in situ LA-ICP-MS trace-element analysis of sulfides, sulfur isotope geochemistry, and LA-ICP-MS elemental mapping of sphalerite, to constrain metal sources, characterize fluid evolution, and establish genetic correlations with the rare-metal system. Key findings include the following: (1) sphalerite shows enrichment in Fe, Mn, Co, and Cd, while pyrite contains elevated As, Pb, Co, Cu, and Mn. Fe, Cd, and Mn primarily occur as solid solutions or nanoparticles, whereas As and Pb exist as micro-inclusions. (2) Sphalerite Zn/Cd ratios (73.6–184) and Co-Ni-As ternary diagrams confirm a magmatic–hydrothermal skarn origin. (3) Mineralization occurred under moderate-temperature, mildly oxidized conditions, as constrained by sphalerite Fe contents and mineral assemblages. Sulfur isotope compositions (δ³⁴S = −1.0‰ to 3.2‰; mean: 1.9‰) indicate a magmatic sulfur source. This study reveals that the Nb-Ta-Rb mineralization, quartz-vein- and greisen-type W-Mo deposits, and skarn-type Pb-Zn orebodies—all genetically associated with highly fractionated granites—constitute an integrated magmatic–hydrothermal system with vertical (depth-related) zoning relative to the granitic intrusion. These results provide critical constraints for understanding rare-metal–Pb-Zn genetic associations and suggest that Pb-Zn mineralization may serve as a key exploration indicator for rare metals in the Lhasa Terrane. Full article

The Huoyanshan Cu-Zn volcanogenic massive sulfide (VMS) deposit, located in the North Qilian Orogenic Belt, China, is of significant economic importance. This study provides new constraints on the ore-forming processes through high-resolution in situ trace element and sulfur isotope analyses of pyrite and sphalerite using LA-(MC)-ICP-MS. Petrographic and geochemical investigations identified three distinct generations of pyrite (Py l to Py III). Early-stage Py I and Py II are characterized by high trace element contents (Au, As, Bi, Cu, Pb), elevated Co/Ni ratios (>1–10), and enriched δ³⁴S values (+4.98‰ to +7.47‰). These signatures indicate precipitation from high-temperature, reduced magmatic–hydrothermal fluids influenced by thermochemical sulfate reduction (TSR). Late-stage Py IIl exhibits markedly lower Co/Ni ratios (<0.1) and lighter δ³⁴S values (+3.72‰ to 3.89‰). This geochemical shift reflects a transition toward a cooler, more oxidized environment driven by the incursion and mixing of ambient seawater as the hydrothermal system waned. Trace element geochemistry of sphalerite reveals an average crystallization temperature of 265.8 °C (derived from the “GGIMFis” geothermometer), consistent with fluid inclusion data and representing a thermal “snapshot” of the waning hydrothermal stage. Systematic discriminant analysis using Ga/In, Ge/In, and Co-Ni-As systematics further confirms a strong magmatic–hydrothermal affiliation. Full article

This study integrates LA-ICP-MS zircon U–Pb ages and the first zircon trace element data from metasedimentary and metaigneous rocks of the Nyong Complex (NyC) in the NW Congo Craton, southern Cameroon, to constrain its petrogenesis, tectonic setting, and crustal evolution. Chondrite-normalized REE patterns show strong HREE enrichment, depleted LREE–MREE, and pronounced positive Ce and negative Eu anomalies, indicating a magmatic origin for the zircons. Trace element signatures suggest that the zircons derived from continental crustal magmas generated under variable oxidation conditions in a long-lived arc-related tectonic environment. Detrital zircon ages range from Archean to Paleoproterozoic, with five major age peaks at 2885 ± 8 Ma, 2775 ± 6 Ma, 2654 ± 7 Ma, 2469 ± 11 Ma, and 2316 ± 11 Ma. These ages correspond to major magmatic and metamorphic events recognized in both the Congo and São Francisco cratons. The preservation of felsic continental crust between 2.9 and 2.2 Ga in the NyC and the Borborema Province (NE Brazil) likely records a critical transition in Earth’s geodynamic regime, marked by enhanced consumption and recycling of mafic crust during Proterozoic accretion compared to the late Archean. This transition reflects the onset of modern-style plate tectonics, enabling craton stabilization and contributing to the assembly of the Nuna/Columbia supercontinent. The NyC is thus interpreted as part of the Trans-Amazonian belt, analogous to that in NE Brazil, and formed during the collision between the Congo and São Francisco cratons. Full article

The Zhongdian Arc is an important copper polymetallic ore cluster in China’s Sanjiang Tethyan Metallogenic Domain, and the Langdu deposit is a representative porphyry–skarn Cu deposit in this region. This study aims to constrain the timing of magmatic activity at the Langdu deposit. It also seeks to reveal the magma’s physical–chemical properties and evolution, and to identify the factors controlling mineralization. To achieve these objectives, this study used LA-ICP-MS zircon U-Pb dating and elemental analysis, combined with halogen and trace element data from apatite. Zircon U–Pb dating shows that the Langdu intrusions were emplaced at ca. 216 Ma in a continental arc setting associated with the westward subduction of the Garzê–Litang oceanic crust during the Late Triassic. Geochemical and mineralogical features indicate that the Langdu intrusions are I-type granite. They originated from partial melting of the mantle wedge metasomatized by subduction fluids. During their ascent, these magmas experienced fractional crystallization dominated by amphibole, titanite, rutile, and monazite. Geochemical records from zircon and apatite further reveal that the ore-forming magma of the Langdu intrusions exhibited high oxygen fugacity (ΔFMQ = +1.53), elevated H₂O content (avg. 7.63 wt.%), and enrichment in S (avg. 560 ppm) and Cl (avg. 2141 ppm). This Cl-rich magma experienced fluid exsolution during its early evolutionary stage. This provided the necessary conditions for metal extraction and transport. In summary, the key factors controlling the formation of the Langdu porphyry–skarn Cu deposit are high-oxygen-fugacity magma enriched in water and volatiles (S and Cl), coupled with efficient fluid exsolution. This understanding is important for better understanding regional metallogeny and for guiding mineral exploration. Full article

Phosphatic deposits from the Lower Cambrian Pedroche Formation (Sierra de Córdoba, Spain) provide key insights into early diagenetic mineralization processes during the Cambrian radiation. This study applies an integrated multi-analytical approach combining Raman spectroscopy, SEM–EDS, LA-ICP-MS, and ToF-SIMS to investigate mineralogical, elemental, and molecular signatures of phosphatized bioclastic carbonates and associated siliciclastic facies from the Los Lagares-1 borehole. Results reveal a systematic phosphatization gradient from carbonate-dominated skeletal rims to phosphate-rich interiors composed of carbonate fluorapatite with variable carbonate and hydroxyl substitution. Trace-element systematics and REE patterns indicate seawater-influenced phosphogenesis under suboxic porewater conditions, coupled to iron reduction and early diagenetic clay mineral formation. In contrast, the siliciclastic siltstone facies preserves poorly crystalline phosphate phases associated with detrital aluminosilicates and chlorite, reflecting distinct porewater chemistry and crystallization kinetics. ToF-SIMS mapping demonstrates spatial coupling between fluorine and phosphate within fossil structures, confirming fluorapatite formation and localized organic matter entombment. These results highlight the strong control of host lithology on phosphate crystallization pathways and trace-element redistribution, and provide new constraints on microbially mediated phosphogenesis in restricted Early Cambrian reef–lagoon systems along the northern Gondwanan margin. Full article

The timing of uranium mineralization in the Xiangshan ore field has long been controversial. Although various geochronometers have been applied by previous researchers, including pyrite Rb-Sr, mica Ar-Ar, and fluorite Sm-Nd, the results remain inconsistent and inconclusive. In recent years, the discovery of abundant Pb-Zn veins in the deeper parts of the Xiangshan ore field has further complicated the interpretation of its metallogenic history. In this study, abundant vein-type hydrothermal apatites closely associated with U-Pb-Zn polymetallic mineralization were identified in both uranium and Pb-Zn ore veins. Combined major-element Electron Probe Microprobe Analysis (EPMA), Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) U-Pb dating, and trace-element analysis were conducted on these apatite grains. The results suggest a mineralization age of 130.9 ± 1.1 Ma for the Shannan uranium deposit, which is consistent with the previously reported apatite U-Pb age of 131.3 ± 7.2 Ma from the Zoujiashan uranium deposit and coincides with the main pulse of volcanic-intrusive activity in the Xiangshan ore field (133–137 Ma). The deep Niutoushan Pb-Zn deposit suggests a younger mineralization age of 124.5 ± 1.3 Ma, which is consistent with a thermal event age of 125.6 Ma determined by zircon fission-track dating and the zircon LA-ICP-MS U-Pb age of late-stage granite porphyry (125.4 ± 1.0 Ma). These ages may constrain the timing of U-Pb-Zn polymetallic mineralization in the Xiangshan ore field. Both magmatic and hydrothermal apatites are classified as fluorapatite and exhibit similar chondrite-normalized rare earth element (REE) patterns. Compared with magmatic apatites, hydrothermal apatites are characterized by elevated Th, U, Ca, and Sr contents, depletion in light rare earth elements (LREEs), Mn, and Na, and distinctly lower Th/U ratios. On major-element variation diagrams, magmatic and hydrothermal apatites define coherent trends but display clear compositional differences related to their formation stages. Apatites from uranium ore veins show strongly negative Eu anomalies and weakly positive Ce anomalies, similar to magmatic apatites. In contrast, apatites from Pb-Zn ore veins display positive Eu anomalies and weakly negative Ce anomalies, with lower Mn and Ga contents and higher SO₃ contents relative to both magmatic apatites and hydrothermal apatites from uranium ore veins. These features indicate that the ore-forming fluids during Pb-Zn mineralization were characterized by significantly higher oxygen fugacity than those during uranium mineralization and magmatism. Combined with published Sr isotopic data for the Xiangshan ore field, we propose that both uranium and Pb-Zn mineralization were genetically linked to the prolonged magmatic evolution of the deep volcanic-intrusive complex. The subsequent incursion of meteoric water modified the physicochemical conditions of the ore-forming system, particularly during the formation of the Pb-Zn mineralization. Full article

The Mahuaping deposit is the largest Be-W-F deposit in the Jinshajiang–Ailaoshan metallogenic belt, Sanjiang region, SW China, with more than 72,700 t WO₃, 41700 t BeO and 2.3 Mt CaF₂. Despite recent studies, the ore-forming process of the Mahuaping deposit remains poorly understood, limiting further insight into its genesis. In this study, a new muscovite Rb-Sr age and elemental compositions of beryl have been reported to constrain the mineralization age and evolution of ore-forming fluids. Muscovite Rb-Sr isochron dating reveals the mineralization age of the Mahuaping Be-W-F deposit is 28.0 ± 1.5 Ma, indicating the formation of the Mahuaping deposit is probably related to the magmatism caused by the sinistral shearing of crust in the Oligocene. LA-ICP-MS elemental mapping and spot analysis suggest the mechanisms for the incorporation of trace elements into the beryl lattice primarily involve two substitution types: Be²⁺ ↔ Li⁺ + Na⁺/Cs⁺ in the crystal core, and Al³⁺ ↔ (Fe²⁺/Mg²⁺) + (Na⁺/Cs⁺/Rb⁺) occurring in both the core and rim. The enrichment of Fe²⁺ is responsible for the blue coloration observed in beryl. The compositional variation from core to rim in beryl crystal indicates the initial ore-forming fluid of the Mahuaping deposit is reducing and acidic, and dominantly originated from magmatic fluids derived from the highly evolved magma. During the evolution, in addition to the continuous mixing of meteoric water, due to pulsating exsolution, the magmatic fluids were also replenished into the ore-forming fluid, enhancing water/rock interaction. Full article

The Yechangping super-large porphyry–skarn deposit is a key component of the East Qinling molybdenum metallogenic belt, central China. Magnetite is widely developed across all mineralization stages of this deposit, yet its systematic geochemical evolution and prospecting significance remain poorly constrained. This study presents in situ major- and trace-element analyses of magnetite via electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and elemental mapping, to unravel the ore-forming hydrothermal evolution and establish reliable prospecting indicators. Four magnetite generations are identified based on petrography and paragenetic relationships: late skarn stage (Mt1), oxide stage (Mt2 and Mt3), and polymetallic sulfide stage (Mt4). Magnetite has total iron contents (TFeO, total Fe calculated as FeO) of 82.72–95.46 wt.% (values above the 93 wt.% stoichiometric limit of pure magnetite stem from minor oxidation), with dominant isovalent Fe³⁺ and Al³⁺ lattice substitution supported by a significant negative Fe–Al correlation. Systematic stage-dependent geochemical variations are observed: Mt1 has the highest Ti (mostly >1500 ppm), V and Cr, while Mt2–Mt4 show progressive Ti depletion (mostly <100 ppm), recording continuous cooling of the hydro-thermal system. V and Cr contents decrease markedly from Mt1 to Mt3, with secondary enrichment in Mt4; Mo concentrations peak in Mt2 (average 5.06 ppm), coupled with elevated chalcophile metalloid Te, As, Pb and Bi. Elemental mapping results show that K occurs as discrete hotspots, which may be mainly derived from feldspar microinclusions, rather than lattice substitution in magnetite. These geochemical fingerprints record a transition from high-temperature magmatic–hydrothermal fluids to late contact-metasomatic fluids, with evolving fluid–rock interaction and oxygen fugacity. Our results demonstrate that magnetite chemistry is a reliable tool for discriminating mineralization stages and vectoring prospecting targets in porphyry–skarn Mo–W systems. Full article

The Jiangnan Orogenic Belt is a world-renowned metallogenic region for Au-W-Sb mineralization, with the Wangu deposit being a representative one. Previous research has demonstrated that tungsten in this Au-W-Sb deposit is sourced from the hosting metasedimentary rocks, but the specific mineral that provides tungsten is still unclear. This study evaluates the tungsten source by conducting petrographic observations and geochemical and geochronological analyses on the rutile from the host slate the Wangu deposit. The results show that rutile from wall rocks of the Wangu deposit yields an age of 955 ± 13 Ma, which is older than both the ore-forming age of the deposit and the age of the host strata. Electron microprobe analyses (EMPA) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) elemental analyses show that detrital rutile is enriched in elements such as Fe, Cr, V, and W, as well as high-field-strength elements (HFSE) including Nb, Ta, Zr, and Hf. The total rare earth element (ΣREE) ranges from 3.37 ppm to 156.85 ppm. The samples are generally enriched in light rare earth elements (LREEs) and exhibit distinct negative Eu anomalies. These geochemical features and a geochronological age of 955 ± 13 Ma suggest that the rutile is of detrital origin and they are possibly derived from the Grenvillian rocks. It is concluded that the detrital rutile in the metasediments could be an important source for hydrothermal tungsten enrichment. Full article

The Circum-Rhodope Belt fringes the Rhodope and Serbo-Macedonian zones in the Alpine orogen of the northern Aegean region. This belt contains Late Paleozoic and Mesozoic metasedimentary successions that record depositional history along the continental margin of Eurasia. Critical successions of the eastern Circum-Rhodope Belt, such as those exposed in the Fanari and Petrota areas, are studied here, integrating their structure, whole-rock geochemistry and U-Pb LA-ICP-MS zircon geochronological context. The Fanari turbiditic succession contains quartz arenite, while the Petrota succession consists of Fe-rich shale and sandstone, and both successions are distinguished by REE-depleted and REE-enriched characteristics and acidic and intermediate arc-related sedimentary sources, respectively. Detrital U-Pb zircon geochronology reveals a Late Carboniferous–Early Permian maximum depositional age of 301.2 ± 8.4 Ma for Fanari quartz arenite and a Late Jurassic maximum depositional age of 147.0 ± 2.0 Ma for Petrota Fe-shale. The results are interpreted in terms of Late Paleozoic continental slope deposition of the Fanari succession along the Eurasian margin and trench-arc sedimentation of the Petrota succession linked to the development of a Jurassic island arc system pertinent to the eastern Circum-Rhodope Belt. These tectonic settings and depositional environments can be used to restore an overall picture of a Late Paleozoic to Mid-Mesozoic sedimentation at the Rhodope–Serbo-Macedonian continental margin of Eurasia. Structures that developed in greenschist facies conditions and N-directed kinematics of the studied successions unequivocally relate them to other units of the eastern Circum-Rhodope Belt and its Late Jurassic tectonic evolution. Full article

The Xinqiao Cu-S polymetallic deposit is located in the Tongling ore concentration area of the Middle-Lower Yangtze River metallogenic belt. The orebodies consist of skarn orebodies and stratiform sulfide orebodies, but the genetic link between them remains controversial. In this study, magnetite was used as a proxy to systematically constrain the hydrothermal evolution from the intrusion to the contact zone and further to the stratiform orebodies. A representative drill hole (E603) was logged, and samples were systematically collected from the Jitou pluton outward to the contact zone. Composite samples from the 8–28 m interval were crushed and prepared as resin mounts for integrated TIMA automated mineralogy, BSE textural observation, and in situ LA-ICP-MS trace element analysis. Five types of magnetite (Mt1 to Mt5) were systematically identified. Mt1 occurs as inclusions within feldspar in the quartz monzodiorite. It exhibits typical magmatic magnetite characteristics and contains grid-like ilmenite exsolution, indicating crystallization during the late magmatic stage. Mt2 is distributed in the interstices of magmatic minerals, commonly showing hematitization and replacement of ilmenite exsolution lamellae by titanite. Its trace element geochemistry displays magmatic–hydrothermal transitional features. Mt3–Mt5 in the skarn and stratiform orebodies are paragenetic with retrograde alteration minerals (e.g., epidote, chlorite, and actinolite) and sulfides, and are characterized by low Ti, Al, and V contents and high Mg, Mn, and Sn contents, indicating a hydrothermal origin. From Mt3 to Mt5, (Ti + V) and (Al + Mn) decrease, while Zn and Mn increase, accompanied by a decrease in the (Si + Al)/(Mg + Mn) ratio. This reflects a trend of decreasing fluid temperature and progressively enhanced wall-rock buffering. The Mg-in-magnetite geothermometer yields relatively consistent results for Mt1–Mt3, but anomalously high temperatures for Mt4–Mt5. This suggests that the elevated Mg activity in the fluid, caused by reaction with carbonate wall rocks, can significantly influence the calculated temperatures. Therefore, this geothermometer should be used cautiously for magnetite in the outer skarn zone and interpreted in combination with other temperature constraints. The textures, paragenetic mineral assemblages, and trace element characteristics of magnetite collectively reveal a continuous mineralization process linking the skarn and stratiform orebodies at Xinqiao, providing robust mineralogical and geochemical evidence for the contribution of Yanshanian magmatic–hydrothermal activity to the stratiform mineralization. Full article

The geochronological framework of the Late Mesozoic volcanic succession in the Great Xing’an Range is crucial for understanding the tectonic regime transition in Northeast Asia. However, the ages and stratigraphic relationships of key volcanic units remain poorly constrained. This study presents zircon LA-ICP-MS U–Pb geochronological data from volcanic rocks above and below the basal unconformity of the Longjiang Formation in the Zhalantun–Jalaid Banner area, central Great Xing’an Range, aiming to determine the timing of volcanic activity, constrain the formation age of the unconformity, and explore its regional tectonic implications. The volcanic–stratigraphic succession in the study area, from base to top, comprises the Baiyingaolao Formation, the basal andesitic conglomerate of the Longjiang Formation, and the Longjiang Formation andesites. Geochronological results indicate that the underlying rhyolitic tuff of the Baiyingaolao Formation yields an age of 130.0 ± 0.1 Ma. Within the andesitic conglomerate overlying the unconformity, andesitic clasts yield an age of 135.8 ± 1.1 Ma, whereas the matrix provides a youngest detrital zircon population age of 130.7 ± 1.0 Ma, constraining the maximum depositional age of the conglomerate. The overlying andesite of the Longjiang Formation gives an eruption age of 125.6 ± 0.8 Ma. These data indicate that the main phase of Longjiang Formation volcanism occurred at ~125.6 Ma, and the basal conglomerate was deposited after ~130.7 Ma. Combined with the ~130 Ma age of the underlying Baiyingaolao Formation and the presence of weathering crusts and erosional surfaces between the two formations, the sedimentary hiatus and exhumation event represented by this unconformity are precisely constrained to have occurred between ~130 Ma and 125.6 Ma. The timing of this unconformity closely coincides with the regional transition in magmatic assemblages from bimodal to andesitic compositions, suggesting that it records a significant tectonic adjustment event in the Great Xing’an Range during the middle to late Early Cretaceous. This finding provides key chronological evidence for understanding the episodic tectonic evolution of Northeast Asia during the Late Mesozoic. Full article

The Jiaodong gold-mineralized area is one of the most significant gold districts in China. The newly discovered Moshan gold deposit is hosted in the Late Jurassic Queshan granite, previously considered a prospecting blind zone. In this study, pyrite from the Moshan gold deposit is examined as the primary research subject. To elucidate the ore-forming processes and genetic mechanisms of this deposit, we conducted a comprehensive mineralogical and geochemical study on pyrite, the principal gold-bearing mineral. EPMA and LA-MC-ICP-MS analyses reveal that the pyrite is slightly sulfur-deficient (average S/Fe ratio of 1.976) and exhibits trace element variations (As, Co, and Ni) strongly correlated with distinct metallogenic stages. Gold occurs in various forms, including visible inclusion gold, fracture gold, and invisible nano-particulate gold (Au⁰). The in situ sulfur isotope δ³⁴S values range from 7.11‰ to 9.40‰ (average 8.00‰), displaying high homogeneity and a positive deviation from the troilite in the Canyon Diablo iron meteorite. By integrating pyrite S-Fe relationships, Co-Ni-As systematics, and sulfur isotope characteristics, the study indicates that the Moshan gold deposit originates from a magmatic-hydrothermal source. The ore-forming materials predominantly derive from Mesozoic granite-derived magmatic-hydrothermal fluids, with a minor contribution from crustal basement materials. The depth of mineralization is interpreted as mid-shallow. These findings not only highlight the metallogenic potential of the Queshan granite and clarify the genetic relationship between the Moshan gold deposit and other regional gold deposits but also provide a novel theoretical foundation and technical support for deep gold exploration in the Jiaodong region. Full article

The Duobaoshan porphyry copper–molybdenum deposit is located in the Great Xing’an Range, eastern segment of the Xing-Meng orogenic belt. It is the largest porphyry Cu-Mo deposit in NE China. Based on the contact relations of intrusive rocks and the results of LA-ICP-MS zircon U-Pb ages, we found that there were five stages of magmatism in the mining area, including the Early Ordovician (478.1 ± 3.2 Ma) granodiorite, the Middle Ordovician (462.1 ± 3.3 Ma, 459.5 ± 2.3 Ma) granodiorite porphyry, the Late Triassic (226.3 ± 0.4 Ma) oligoclase granite, the Middle Jurassic (170.1 ± 5.6 Ma) andesitic porphyrite, and the Early Cretaceous (118.1 ± 6.6 Ma) diorite. The Early and Middle Ordovician granodiorite and granodiorite porphyry are the principal host rocks for the mineralization in the deposit. However, Cu-Mo mineralization was also observed within the Late Triassic oligoclase granite, indicating that there are two stages of Cu-Mo mineralization in the Duobaoshan deposit. Combined with the previously reported Late Triassic skarn Cu mineralization occurring in the Xiaoduobaoshan deposit, and the Early Jurassic skarn Cu mineralization in the Sankuanggou and Yubaoshan deposits, we conclude that there are four metallogenetic stages in the Duobaoshan ore-concentration area. Regionally, there are five stages of Cu-Mo mineralization occurring in the northern Great Xing’an Range, including the Ordovician, Late Triassic, Early Jurassic, Late Jurassic, and Early Cretaceous. After discussing the tectonic setting for the generation of these deposits, we propose that the Duobaoshan ore-concentration area was influenced by the subduction of the Paleo-Asian Ocean, Mongol-Okhotsk, and Paleo-Pacific Plates during the Phanerozoic. Full article

Pegmatites with miarolitic cavities have not previously been reported from the Larsemann Hills, East Antarctica, and their age and origin remain poorly constrained. We report the first geochemical and geochronological data for fluorapatite from a newly discovered pegmatite with miarolitic cavities in the Larsemann Hills. Large Fe-rich fluorapatite crystals (up to 5 cm) contain abundant oriented monazite-(Ce) inclusions and display elevated REE (1397–7966 ppm), relatively high Y (945–4192 ppm), and low Sr (52.2–83.5 ppm). Their trace-element signatures plot within the fields of partial melts, high-grade metamorphic rocks, and evolved fluid-rich magmatic systems. U–Pb dating of fluorapatite yields concordant ages of 519 ± 4 Ma (ID-TIMS) and 521 ± 31 Ma (LA-ICP-MS), indicating crystallization during the D₄ stage of the Pan-African orogeny. The isotopic equilibrium between apatite and monazite inclusions suggests synchronous formation and late-stage fluid overprinting. Combined geological, geochemical, and isotopic evidence shows that the pegmatite formed in situ as a product of anatexis of the Broknes paragneisses and evolved within a volatile-rich magmatic–hydrothermal system. These results provide the first direct age constraints on pegmatites with miarolitic cavities in Antarctica and shed new light on the final stages of East Gondwana assembly. Full article